My '05 5 speed Vibe is approaching its one year anniversary (approximately 15k miles). This past year I have used M1 5w30, GC and M1 0W-30. According to Terry, GC gave the best UOA of the three. Next month it will be convenient to do an oil change. Is it worth the trouble to keep experimenting ie give a go with PP 5w30 or the XD or should I just settle on the GC?